We haven't seen the new Nets super team in action yet, so to say that they're going to be the second-best team in the conference behind the Heat is unfair to the Chicago Bulls, Indiana Pacers and even the New York Knicks.
It all depends on how well this team can play together and the chemistry they develop over the course of the season. They could start off slow like the 2010-11 Heat team and then rapidly improve as the season progressed, or they may never find that rhythm and teamwork and end up like the 2012-13 Lakers, who barely even made the playoffs.
However, I expect this Nets team to finish as one of the top-four seeds in the East. Although it doesn't seem like much of an expectation, as the Nets finished fourth in the conference last season, but teams like the Bulls and Pacers are bound to keep improving and getting better as well.
If the team gels faster than expected, then the Nets can probably finish with the second seed, over the Bulls, Pacers and Knicks, but behind the Heat. In any case, expecting the team to be one of the top four in the conference is realistic and nothing extraordinarily shocking.